Re-Build Scope Thought Process

[RandalJ]

I have owned an 86 Carrera for a little over a year now. Going into the purchase, I knew (from PPI) that the #6 exhaust valve guide was worn. The PPI shop, who is highly reputable, said my problem did not appear to be dire. In fact, they recommended re-doing a leakdown test after another 15kmi and seeing how worse it gets.

The car had let out a moderate puff of smoke when I come to a stop, since day one, but it has not gotten worse. Driveability is excellent. Oil consumption is a concern, a bit above maximum allowed, but has not gotten worse.

The car is my daily driver, and I have gone about 10k miles since the inspection, with just over 80k miles on it now.

Anyway, after reading through Wayne's 101 Projects and 911 rebuild books, which I recently purchased. I have begun to consider doing the work myself.

My question is about the process of deciding how far to go in the tear-down. Does it make sense to stay focused and just do a top-end job? That is, get the engine out, get the heads off, but leave the cylinders in place, just going after the known problem? Or do I tear everything apart, crack the case, and at least have everything inspected?

Wayne's opinion seems to be that 90% (or something like that) of the teardown is done once you have the heads off, so you might as well go all the way.

I, however, am addressing a specific problem - going through the expense of machine shop work, new valves, guides, maybe springs - who knows? And like most of us, have limited time and funds.

My question is whether it makes sense to stop there, or would it be foolhardy not to at least pull the cylinders off, and inspect the pistons and cylinders?

And then maybe the rods, and, what the hell, crack the case. But then I see the cost in terms of my time and the complexity rapidly mounting. And with the 3.2's reputation for durability, I might do all that work for nothing other than to know the engine situation more thoroughly - minus any f%&*up during the re-assembly, of course.

I'll probably try to tackle this within a year or so, and I want to gear up mentally and finacially based on the scope of the re-build.

I guess I know some answers to expect, like "inspect and fix as much as you can afford to do". But I'm looking for guidance on what you'd do given the known need for a valve job and the mileage. Comments like:

"if you do the heads, inspecting the pistons and cylinders are a must, since it isn't that much additional effort. Leave the case intact unless you know there is obvious damage, want to fix a leak, or have 200k miles and never changed the oil... etc."

or

"Tear everything down to the last nut and bolt. Inspect and re-work or replace as needed, even if you cannot afford it."

Thanks

[Tim Walsh]

How many miles ARE on the engine?

[emcon5]

And how much oil does it burn?

Tom

[RandalJ]

The engine just tuned over 80k miles this week.

I don't have the exact oil burn rate, but my rough guess is a 1.5 quarts per month, or per about 750 miles, which works out to 2 quarts per 1000 miles.

[HarryD]

Ultimately,the decision is your to make.

A few things to consider:

-If you rebuild the top end only, you may strenghten it to the point it accererate the bottom end failure modes.

-If you split the case, you may need to align bore the case to get the halves to align properly (more of a concern on a magnesium case).

-While not "much more" than a top end alone, the cost is higher and your wallet will be adversely impacted.
-If you pull your pistons and rering, you will need to have the rings seated which somethimes can be a problem.

-Based on anecdotical (sp) information, I think you bottom end is "supposed" to last for a long time.

Before you decide, you may want to do some more tests such as compression and leakdown to see if you need to replace your rings. Get your oil tested to see if bits of your main bearings are showing up in the oil (you will need to be careful with these results as some material may be normal).

You may, after testing and thinking about what you want to do, start with a top-end only. When the heads are off, inspect the cylinder bores carefully for signs of damage. Pull a piston/cylinder and inspect the rod bearing to see if you have any wear. Based on these findings, decide how much further to go.

Your money, your choice.

FWIW, I had severely worn valve guides on my 116k 2.4L engine and based on the top end tear down, decided to just do the heads. Why? Cylinder bores looked great, no external evidence of other engine problems, and did not want to risk need for align bore due to magnesium case. After 2,000 miles, all is ok and no leaks. I figure that I will know the "real" story after 15-20k miles (2-4 years fo driving for me).

good luck.

[Fishcop]

I originally intended to only do the top end of my motor. By the time I was down to the p&c's it was so close to being completely pulled down, I thought what the hell.

Man am I glad I did! My bearings were showing copper, I was missing several teeth from a chain wheel on the intermediate shaft, and there was some minor scoring on the crankshaft. All these thing are now fixed. For what has amounted to only an extra $600 dollars or so, I can at least have peace of mind.

[RandalJ]

Fishcop and HarryD, thanks for your stories. Perhaps it's one of those things that you decide when you get there, based on how difficult the process was, and the general state of things as you start to "peel the onion".

Oh, and the money...

Fishcop, was the engine you were dealing with the original '69? If so, how many miles on it when you tore it down? As Harry pointed out, if the engine had relatively low mileage, and was well maintained, perhaps the top end would suffice. A high mileage, older engine would obviously merit a closer look.

[ChrisBennet]

I know I'm the minority here but I think that people are glossing over what is involved in "doing the bottom end while you're in there". I agree that it should be done but I think we need to clarify what's involved.
If all you are doing is replacing the bearings and seals it's not a big deal - but that isn't a true rebuild either. Jim Pasha calls this sort of thing an "overhaul". An overhaul is a rebuild minus the machine work - rods aren't rebuilt, rockers aren't rebushed, case isn't decked, etc.
-Chris

[Rot 911]

Randal do a search for some of my more recent threads on the 3.2 I am presently rebuilding. It has 133,000 miles on it. I was burning 1qt every 400 miles. Leakdown test showed burned #5 exhaust valve. I decided to do a complete rebuild. However other than needing my heads (all 6) rebuilt the rest of the engine looks like it just came from the factory. No wear at all on the cylinders (can still see the hone marks) all bearing showing no wear, same with all the gears. If I had to do it all over again on an engine with only 80K miles I would probably just do the top end.

[Superman]

Split the case and replace those wimpy rod bolts. Put new bearings in and go. Align boring is just not necessary with an AL case engine. One thing I wish I had done but did not, was to re-bush the rod small ends. The wrist pin bushings. My bearings were showing copper too. At least the intermediate shaft ones were. All I did was replace the bearings. Glad I did. Easy.

[hobieboy]

I am in exactly same boat, though my engine seems quite healthy - not burning excessive oil; and everything runs fine; though leak down & visual inspection said that my #6 exhaust valve is probably gone.

I agree with ChrisBennet that more I look, bottom end rebuild will be very $$$ - new rods, bearing, ... and then there's the cost of rings or even new pistons (god forbid) once I go beyond the top end.

And don't forget that its sooooo easy to upgrade while you are there

Just me 2 cents...

[Fishcop]

Randal, I guess Chris is right with the term "overhaul". You just won't know without looking. All I can say relates to my experience, and I still haven't finished. I have had my case time-certed and decks machined along with fly cutting of the through bolt holes.

There is no question in my mind that the bottom end of my engine would have failed in the short term had I not taken to time and extra expense to split the case as I was on copper for nearly all bearing surfaces (not to mention probable cam chain sprocket failure).

This is a second engine ('75 2.7 80,000 miles) I purchased a while back (My car is still running it's original '69 2.0 with 120,000 miles), so I have not got time issues and can go at my own pace. On the good side... the crankshaft has been measured as standard/standard and is crack free, the rods are fine (although I'll be taking Superman's advice and have the little ends rebushed), and I have had the case upgraded to the later oil bypass spec.

I don't feel all this has dramatically increased the cost of my over all rebuild as new rod bolts and nuts are relatively cheap, case sealant won't break the bank, bearings... cheap, crack testing and micropolishing of crank was.... cheap. When I refer to cheap, I mean less than $100 Australian.

[toolman]

The bottom end of the Carerra engines are pretty bullet-proof since they use the same one on the turbos that have a lot more stress on them. I had a huge oil use problem with my 87, 1 qt every 200 miles. It was all due to the valve guides that wore out at 75,000 miles. I chose to install new P/C's "while I was in there" and had the heads rebuilt. I alway had great oil pressure so I left the bottom end alone. It runs great and very strong so far, I don't feel I will ever have a problem.

[RandalJ]

Thanks for all your reponses. Since my known issues are similar to yours, toolman, my hunch is that I'll probably get down to at least the piston/ring/cylinders/rods inspection stage, and do what needs to be done, and only crack the case if there is compelling evidence that I need to go further. I'm sure I'll be back when the time comes...

[toolman]

Sounds like a plan, I didn't even check my rods though.

[MoreGAS]

RandalJ,
You can take it in a step by step approach. A leakdown will tell you whether you have leakge through the piston rings(listen through the crankcase breather or put a lighter in frt of the line removed from the oil tank. If you feel a bunch of air there on the cylinders that are leaking down poorly- you need to pull the P/Cs and measure the cylinders for ovality and taper, and the pistons' top ring land gap with a NEW ring. If you have the Kolbenschmit(sp?) pistons and cylinder just toss them in the trash. I have seen atleast 4 different engines with these that had broken ring lands. These were often used as a stop-gap measure in production when Porsche ran out of Mahles I was told. These are common in 1987 engines.

You will have to pull all the heads apart and do a head rebuild with all new (proper material)guides. We had an orig. 85 3.2 at the track last weeekend with 180,000 miles on it (set in race trim with custom headers and chip- making 203 to the wheels) using 1/2 qt every 20 min's! The thing puffed some light smoke on decel form the shot guides. Now that the season is over the owner will have us do it all up rightouse. So the point is you will not likely hurt the engine running it with heavy oil use as long as you replenish it. Next step is to put rebuilt rods in there with a resized big and small end(with proper small bushings made from better material than the bronze and steel backed stk ones-no good) and ARP rod bolts. The stk bolts are poor and if one goes form a misshift or backhole stretch it is catastrophic and you'll be on the classified lists hunting down an oil pump, case, cranks....
You can change thoese rods and bolts through the spigot bore holes in the case without splitting it. This also affords you a look at the condition of the rod bearings. You'll replace those for sure but if they are at all marginal-split the case and sniff out the mains.

Oil pressure is not the criteria to determine if bearings are healthy. Debris kills them as well as at one time in their life running low on oil. Best policy is to drain your oil in a perfectly clean pan when you change it and always inspect it and the magnets very well. Also cut open the oil filter and see what has been through it.

This will be a thourogh approach to doing your engine yourself. Then, next toughy is: deciding what you want to tweek and upgrade as a guy couldn't possibly do all this work and put it back stock-could you? Atleast put in the euro P/C set if yours are worn out!

Good Luck,
Kevin Roush
GAS Motorsport
Performance Porsche
909 985 2909

[RandalJ]

Kevin - thanks for taking the time to respond. And Wayne, thanks for the notification feature on this forum - otherwise I might not have come back to this thread.

Anyway, just to go into a bit more detail on the PPI compression and leakdown tests that were performed. The shop, Stuttgart Southwest, in Tempe AZ, found the following:

Cyl Compression Leakdown
1 160 4%
2 160 3%
3 160 3%
4 155 4%
5 160 4%
6 150 28%

At first they suspected a broken ring on #6, but they went to great lengths to determine what it really was.

They first adjusted the valves on 4-6 to rule out either valve on number 6 being too tight and not allowing a valve to properly seat. Results were unchanged.

As you mentioned, there are various orifaces that you can listen through to determine what's leaking. Turns out they had to pressure #6 up very high in order to discern the leak source. They did heard it throught the exhaust, leading them to conclude that it was #6 exhaust.

I forget how they ruled out broken rings, but it was probably from listening through the crankcase breather, as you mentioned.

At the time I remember thinking that this was a showstopper, but the shop owner told me that this was not necessarily an indication that an immediate re-build was in order. He said that he had seen cars in this situation go another 15k, 30k even 45k miles before the situation deteriorated significantly. His advice was that since overall the car was in really great shape, that it was a keeper that should be tested again at these intervals. He said he wouldn't think twice about driving to the East Coast and back, given its current condition.

But he said to plan on spending $3-5k in the next 2-5 years for this work.

I bought the car, using this condition as some negotiation leverage, and have put on about 10k miles (just turned 80k total) over the 15 months of ownership. I think I mention before that this is my daily driver, 20 miles round trip to work plus frequent lunchtime errands. So that is well over a round trip to Maine and back so far.

But I will say one thing. I have been very attuned to engine sounds, and have been somewhat paranoid about anything going wrong. On the other hand, here is an 18 year old car doing the chores of any late model car with no fuss. So I have very gradually learned to relax with it.

Were it not for the puff of smoke I typically get when I come to a stop - typically at intersections after cruising at 45 - 50 on city streets, or the oil consumption, I would not think anything is wrong. The engine seems strong as an ox, and has not emitted any strange noises so far - even up to redline.

I even did a two-day DE a year ago with no problems.

Its funny about that smoke. If I have the targa top on, I hardly notice it, even with the windows down. With the top off, the smoke sometimes comes cascading over me like a big wave crashing down on a surfer from behind. It's not a steady smoke, just a brief burst when I come to a stop. I don't seen to have it when I am in motion, letting off the throttle.

Anyway...

One other issue that I have had is some detonation under high load throttle conditions during summer, which is tied to the hot intake temps when running the A/C, coupled with the advanced timing of an Autothority chip (a previous owner installed the Autothority MAF). So, for sure I'll be looking at the P's and C's for signs of damage. And may need to relocate the condensor from the engine lid to somewhere else.

The rod bearing and bolt advice is good, too, and probably not much extra in time or money.

Performance mods? I hate to even think about them...

[Larry Harris]

Kevin Roush,
Are you located in Ontario, Ca.. If so, what type of services do you offer.

Thanks
Larry H.

[MoreGAS]

RandalJ,
I have had similar experiences with a couple Autothority chips. Make sure you go to a cooler sparkplug (especially in your climate) like a Bosch W5 from a 7, maybe a 4 in the summer. -good luck.

Larry Harris-Nearly-I am in upland Ca. In a nutshell,we build ,service, dyno tune, configure 911's(95%) for performance driving,this can embrace street cars too. This means, roll cage,header&sheet metal fabrication, car rebodying, engine and transmission building, Engine management installations and development, suspension development,....the fun stuff. We also provide trackside support and driving development at the POC and PCA events we attend. We try to avoid oil changes and tune-ups (you know where a shop makes easy money fast) and do what interests us. We also sell parts and accessories(say to folks on this board who may want to dig-in themselves) coupled with 15yrs experience tuning,buildng and racing these cars.

Happy Motoring,
Kevin Roush
GAS Motorsport
Performance Porsche
909 985 2909

[Wayne 962]

One quart of oil every 500 miles is way too much - the factory spec is insanely off on this number. Anything less than a quart per 1000 is suspect.

My mood changes daily, but it sounds like you might be on the borderline here. For you, I would recommend removing the top end, the cylinders, and replacing the rod bolts without splitting the case. 80K miles is probably good enough, although if you find signs of abuse in the engine from dirty oil (check the cam towers bearings, as shown in the book), then you should replace the main bearings. Rod bolts should be replaced, and can be swapped out without splitting the case (contrary to comments above). This is an area of great concern for the 3.2s...

-Wayne